[AMRadio] Local oscillators and TVI


Jim Miller WB5OXQ wb5oxq at grandecom.net
Sun Mar 5 11:52:22 EST 2006


When I was in high school in the mid 60s a friend bought a older multiband 
console radio,  RCA model 15K built in 1937.
This was a real good sounding console with a tuned speaker compartment 
housing a 12" EM speaker which must have weighed 30 pounds.  The receiver 
had 15 tubes and push pull 6L6 output so it was healthy to say the least. 
The most interesting band was in the 40-60mhz range which could pick up the 
highway patrol broadcasts.  I now know that was probably supposed to be the 
original FM band that was before they moved it to 88-108mhz.  Anyway those 
radios had no internal antenna and needed a piece of wire attached to the 
antenna terminal for best reception.  We found that an old outdoor tv 
antenna worked real well for reception on the fm band.  I would visit at 
this home at night after supper and we would listen to the police calls for 
a long time.  We soon began to notice the neighbors would have the mobile tv 
repair truck at their house regularly.  I wandered over to listen to the 
conversation the neighbor was having with thje tv repariman as he was 
leaving their house.  It seems that their tv played well in the daytime and 
the repariman could find nothing wrong but ths neighbor told  him that after 
the evening news, they could barely pick up any stations at night (using 
rabbit ears).  That is when we learned about local oscillators.  Since there 
were no tv sets in 1937 and probably no FCC regulations about harmful 
radiations the set was a real good transmitter on the low band channels. 
Our local NBC station was channel 3.  I guess using a tv antenna for an 
external antenna on the old RCA really helped make the transmitted signal 
even stronger!  We found that funny and made a paper label and gluded it to 
the back of the radio stating that "This receiver DOES NOT conform to part 
15"!!!
Later we built a AM broadcast transmitter using a single 6L6 but that was 
short lived and we never got caught.
Jim in Waco, WB5OXQ 





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